Subsets can be found on the right side of the in the search bar in the header on the Portal. This controls which set, or "subset" of events is displayed and searched using the other search parameters. The default option is "All Events". Other universal options include:
Virtual Events
Editors Picks
Bookmarked
Any publisher that is also using CitySpark ticketing will also see an "Our Tickets" option.
A standard, non-universal option is "Free Events" which can be created using the URL adding the parameter "subset=free" to the URL
You can also create any additional custom subsets you wish by using labels. Just add the labels you wish to include as subsets to the portal in the admin portal settings. Admin > Portals > View Portals > edit portal > Content & Submission Settings > Labels for Subset Filters.
Any labels added there will display the label "display name" in your subset drop down, and be available for URL creation using the parameter "subset=[system label name]". Keep in mind that only 10-12 characters will display effectively in the UI, so display name brevity is important.